This invention relates to gating for medical imaging, and more particularly, this invention relates to a method and system of selecting an arbitrary cardiac phase in physiological, non-electrical signals for cardiac gating.
In many applications, it is often desirable to obtain an image at a particular point in a variable cycle, such as a peak of the variable cycle, to analyze behavior at that peak. In the medical field, imaging systems are often used to obtain internal physiological information of a subject. For example, a medical imaging system may be used to obtain images of the bone structure, the brain, the heart, the lungs, and various other features of a subject. Medical imaging systems include magnetic resonance imaging (MRI) systems, computed tomography (CT) systems, x-ray systems, ultrasound systems, and various other imaging modalities.
Gating is essential for characterizing different attributes of a dynamic organ during imaging. The most common techniques of gating including cardiac, respiratory, and peripheral pulse gating have uses in numerous medical applications across diagnostic modalities including CT, MR, X-Ray, Ultrasound, and PET-CT.
Cardiac gating is an essential component of cardiac imaging while using imaging modalities such as CT, magnetic resonance (MR) to minimize motion related artifacts. Current cardiac imaging tools utilize simultaneously collected EKG data to tag CT projection data with cardiac phase information. Essentially, the R-wave of the EKG is used for this purpose. Heart functions are characterized by two distinct periods called systole and diastole. In systole, the heart-muscle is contracting the volume of the left ventricle to pump the contents out through the aortic valve. During the diastole, or diastolic period, the left ventricle is filling through the mitral valve. At the end of the systole, the left ventricle has its smallest volume since it has been contracted to pump blood out. The end of the diastole is the point at which the left ventricle has its largest volume since it is filled with blood ready to be pumped out. During the diastolic period the heart is relatively motion-free allowing images generated from data collected during this period to be clearer as a result of the limited movement.
FIG. 1 illustrates one cardiac cycle of an EKG signal waveform, including a systole condition, or period, and a diastole condition, or period, of the heart. The portions of the EKG signal labeled Q, R and S are referred to as the QRS complex, in which the R-feature, or R-wave, is the most prominent, highest amplitude, feature of the entire EKG signal. The cardiac cycle is typically defined as beginning with an R-wave and continuing until the occurrence of a next R-wave.
EKG gating selects times when a best image of the heart is available. An EKG machine is connected to a patient. A cardiac cycle period is determined, for example, as a time between R-peaks of the EKG. One of the common applications is to use an R-peak as a reference along with the determined cardiac cycle period, to acquire gated images during periods of a cardiac cycle for which the heart is nearly stationary, or during periods for which imaging is desired.
Turning now to FIG. 2, two of the commonly used approaches, shown collectively at 130, for determining the diastole and systole phases in a cardiac cycle using an EKG signal are shown. In waveform 132, the systolic 134 and diastolic 136 phases are centered at x % and y %, respectively in a cardiac cycle. In waveform 140, the systolic phase 142 is certain delay from the previous R-peak 146. Similarly, the systolic phase 144 is certain delay from the previous R-peak 148. The diastolic phase 152 is certain advance from the next R-peak 148, and similarly, the diastolic phase 154 is certain advance from the next R-peak 150. These approaches 130 are based on an assumption that the cardiac phases would occur at a certain time interval during the cardiac cycle. This assumption may not necessarily be accurate for every cardiac cycle and for every individual in a population.
Once the location for the systolic and diastolic phases are made or estimated using one of the approaches described above in FIG. 2, image reconstruction may be performed. FIG. 3 shows half scan and multi-sector image reconstruction where xe2x80x9cIxe2x80x9d represents the image reconstructed from a single cycle and two consecutive cycles respectively. In waveform 122 of EKG waveforms 120, projections 126 from a single cardiac cycle, also known as half-scan reconstruction, for a dataset for reconstruction. In waveform 124, subsets 128 of projections 126 from multiple cardiac cycles are blended, also known as sector based reconstruction, to form a complete dataset for reconstruction.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method of selecting an optimal trigger point in a cardiac cycle, the method including providing an input signal including non-electrical cardiac related data, analyzing the input signal to detect candidate features, sorting through the candidate features to select optimal features, and selecting an optimal trigger point.
In another embodiment, a method of selecting an arbitrary cardiac phase for cardiac gating includes identifying a trigger point identifying onset of a systole or diastole phase on a signal, the trigger point existing at time t1, specifying a time xcex4 t before the trigger point and extending from a time t0 to a time t1, wherein time t0 is earlier than time t1, and selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t0 to a time t2, wherein time t2 is later than time t0.
In another embodiment, a method of image reconstruction using cardiac gating includes providing a signal indicative of a plurality of consecutive cardiac cycles, for each cardiac cycle, the method further including identifying a trigger point identifying onset of a systole or diastole phase, the trigger point existing at time t1, specifying a time xcex4 t before the trigger point and extending from a time t0 to a time t1, wherein time t0 is earlier than time t1, selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t0 to a time t2, wherein time t2 is later than time t0, and reconstructing an image over at least one time interval T.
In another embodiment, a storage medium is encoded with a machine readable computer program code, the code including instructions for causing a computer to implement a method for selecting an optimal trigger point in a cardiac cycle, the method including providing an input signal including non-electrical cardiac related data, analyzing the input signal to detect candidate features, sorting through the candidate features to select optimal features, and selecting an optimal trigger point.
In another embodiment, a storage medium is encoded with a machine readable computer program code, the code including instructions for causing a computer to implement a method for selecting an arbitrary cardiac phase for cardiac gating, the method including identifying a trigger point identifying onset of a systole or diastole phase on a signal, the trigger point existing at time t1, specifying a time xcex4 t before the trigger point and extending from a time t0 to a time t1, wherein time t0 is earlier than time t1, and selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t0 to a time t2, wherein time t2 is later than time t0.
In another embodiment, a system for selecting an optimal trigger point in a cardiac cycle includes a non-electrical sensor sensing mechanical vibrations of the heart, a processing circuit coupled to the mechanical sensor, the processing circuit processing a signal sent by the mechanical sensor, analyzing the signal to detect candidate features, sorting through the candidate features to select optimal features, and selecting an optimal trigger point.
In another embodiment, a system for image reconstruction using cardiac gating includes a non-electrical sensor sensing mechanical vibrations of the heart, a processing circuit coupled to the mechanical sensor, the processing circuit processing a signal sent by the mechanical sensor, identifying a trigger point identifying onset of a systole or diastole phase on the signal, the trigger point existing at time t1, specifying a time xcex4 before the trigger point and extending from a time t0 to a time t1, wherein time t0 is earlier than time t1, and selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t0 to a time t2, wherein time t2 is later than time t0.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.